FAQ
The questions techs actually type into a search bar. Every answer links to a full field guide with the method, the tables, and the standards behind it.
On a fixed-orifice (piston) system, target superheat is typically 10–20°F depending on indoor/outdoor conditions. On a TXV system the valve regulates superheat itself, usually holding 8–12°F — so you verify charge with subcooling instead.
Learn more →Most residential R-410A TXV systems target 10–12°F of subcooling at the condenser outlet. The number on the unit’s data plate or install manual overrides any rule of thumb — always charge to the manufacturer spec when it’s listed.
Learn more →Subcooling. A TXV holds superheat roughly constant regardless of charge, so superheat won’t tell you if the charge is right. Fixed-orifice systems are the opposite — charge those by superheat.
Learn more →A few percent lower than R-410A at the same saturation temperature — at 100°F saturation, bubble is about 303 psig and dew about 292 psig. Because R-454B is a zeotropic blend, use the bubble column for subcooling and the dew column for superheat.
Learn more →No. Pressures run about 5% lower on the liquid side (more on the vapor side), and R-454B has temperature glide, so a single saturation number isn’t enough — liquid (bubble) and vapor (dew) readings differ. Reading it like R-410A will skew your superheat and subcooling numbers.
Learn more →400 CFM per ton is the standard-air baseline, so a 3-ton system moves about 1,200 CFM. Drop toward 350 CFM/ton in hot-humid climates for better moisture removal, and up to 450 CFM/ton in hot-dry climates for more sensible capacity.
Learn more →Using the 20 BTU per square foot rule of thumb, about 40,000 BTU/hr — roughly 3 to 3.5 tons. Ceiling height, insulation, windows, and climate move that number, so treat it as an estimate, not an equipment order.
Learn more →Most straight-cool condensers are 240V loads with no neutral, so 10/2 with ground does the job when the nameplate MCA allows 10 AWG. Use 10/3 only when the unit’s wiring diagram actually calls for a neutral.
Learn more →MCA (Minimum Circuit Ampacity) sizes the wire — your conductor’s ampacity must meet or exceed it. MOCP (Maximum Overcurrent Protection) caps the breaker or fuse size. Both are printed on the condenser’s data plate.
Learn more →The NEC’s informational notes recommend limiting voltage drop to 3% on a branch circuit and 5% combined for feeder plus branch. It’s a design recommendation rather than a mandate in most cases — but exceeding it invites performance problems on compressor starts.
Learn more →BTU load, duct sizing, and the unit converter are free. P-T charts, superheat & subcooling, and NEC wire sizing come with Pro — 3-day free trial, then $4.99/mo or $19.99/yr.
